By way of background, traffic signals are employed to regulate motorists and pedestrians via various commands. These commands are provided by various illuminated elements with particular colors and/or shapes that are each associated with an instruction. Elements were conventionally illuminated via incandescent bulbs, which use heat caused by an electrical current to emit light. When electrical current passes through a filament such as tungsten it causes the filament to heat to the point that it glows and gives off light. Such illumination can be covered with a colored lens and/or template to provide a meaningful instruction that can be viewed in a variety of external lighting conditions.
The filament is a resistive element in the incandescent bulb circuit, and the amount of current drawn by the filament is proportional to its impedance. The impedance increases as the temperature of the filament increases. Thus, a conventional lamp has a larger initial current draw, which drops in proportion to the increase in the filament impedance. This variation in current draw is known, and a predetermined range can be utilized to monitor the lamp operation. As such, a lamp failure condition can be identified based on the amount of current drawn by the filament. For example, if the filament fails (e.g., breaks), the impedance approaches an infinite value and the current value decreases to almost zero. If the current drawn is outside of the predetermined range, a responsive action can be initiated by a current monitor or other control system.
Unlike incandescent lamps, LED lamps consist of an array of LED elements that draw much less power. LED lamps have numerous advantages over incandescent lamps, including greater energy efficiency and a longer lifetime between replacements.
An LED traffic signal generally includes a standard power supply that incorporates a safety circuit. In cooperation with the safety circuit, the LED traffic signal includes an LED current detector that generates a light output emission signal. When appropriate, this signal causes a fuse to blow out within the power supply, which in turn causes an input fuse to blow. As a result, there will be no input current to the LED signal if the LED current drops below a pre-determined LED current level.
Existing traffic controllers, however, were designed for incandescent lamps, which consume between 30 and 100 watts of power. Thus, the safety circuit in the lamp forces a fuse to blow out when the power drawn by the load is lower than a predetermined threshold (for example, 30 watts). However, LEDs generally consume less power than incandescent lamps, usually less than 10 watts. Thus, at 10 watts the traffic controller may fail to work.
One known solution is to increase the power consumption of the LEDs by more than 30 watts. However, this creates thermal issues in the traffic signal and accelerates LED degradation. Another known solution is to modify the input current by adding a special circuit in parallel with the LEDs that emulates higher power consumption. This solution, however, requires a circuit external to the LED signal, wastes energy and introduces false alarms to the field traffic controller. When the input frequency line varies, the emulated higher power consumption changes the angle position and then the controller cannot read it.
Thus, there is a need for an apparatus and method that eliminates the above-discussed drawbacks of the prior art.